> Or at least be stable enough for a Debian or Red Hat to switch to it as a default?
SUSE / openSUSE has had btrfs as the default filesystem for a few years (and we have a bunch of tools built around it adding features like boot-to-snapshot and auto-snapshot of upgrades). Personally I have had issues with it, but I've also messed around with btrfs subvolumes quite a lot (developing container runtime storage drivers) so it might be self-inflicted.
SUSE / openSUSE has had btrfs as the default filesystem for a few years (and we have a bunch of tools built around it adding features like boot-to-snapshot and auto-snapshot of upgrades). Personally I have had issues with it, but I've also messed around with btrfs subvolumes quite a lot (developing container runtime storage drivers) so it might be self-inflicted.